US3796652A

US3796652A - Thermal dehydration of bitumen froth

Info

Publication number: US3796652A
Application number: US00323454A
Authority: US
Inventors: S Lupul
Original assignee: Canada Cities Service Ltd; Gulf Oil Canada Ltd; Imperial Oil Ltd; Atlantic Richfield Co
Current assignee: Petro Canada Exploration Inc; Gulf Canada Ltd; Canada Cities Service Ltd; Imperial Oil Ltd; Atlantic Richfield Co
Priority date: 1973-01-15
Filing date: 1973-01-15
Publication date: 1974-03-12
Anticipated expiration: 1991-03-12
Also published as: CA1010389A

Abstract

BITUMEN FORTH CONTAINING WATER IS CONTACTED WITH HOT DRY BUTIMEN IN A MIXER TO VAPORIZE ALL THE WATER, THE THE MIXTURE IS FLASHED TO REMOVE THE WATER VAPOR AND PRODUCE DRY BITUMEN. PART OF THIS LATTER PRODUCT IS HEATED AND RECYCLED TO THE MIXER.

Description

March 5 LUPUL THERMAL DEHYDRATION OF BITUMEN FROTH I Filed Jan. 15, 1973 BITUMEN FROTH CONTAINING WATER WATER HOT BITUMEN b MIXER FLASH HEATER DRUM RECYCLED BITUMEN i DRY I BITUMEN PRODUCT United States Patent THERMAL DEHYDRA IION OF BITUMEN FROTH Silver Lupul, Sherwood Park, Alberta, Canada, assignor to Canada-Cities Service, Ltd., Imperial Oil Limited,

Aflantic Richfield Canada, Ltd., and Gulf Oil Canada Limited, fractional part interest to each Filed Jan. 15, 1973, Ser. No. 323,454 Int. Cl. C10c 3/00 US. Cl. 208-39 5 Claims ABSTRACT OF THE DISCLOSURE Bitumen froth containing water is contacted with hot dry bitumen in a mixer to vaporize all the water. The mixture is flashed to remove the water vapor and produce dry bitumen. Part of this latter product is heated and recycled to the mixer.

BACKGROUND OF THE INVENTION This invention relates to a process for thermally dehydrating bitumen froth. It finds application as one of the operations in the combination of operations by which bitumen is extracted from tar sand.

A large proportion of the worlds known hydrocarbon reserves exists in the form of tar sand. One large deposit of this material is found along the banks of the Athabasca River in Alberta. The tar sand comprises water-Wet grains of sand sheathed in films of bitumen. In treating the tar sand to recover commercially saleable products, it is first necessary to separate the bitumen from the water and sand.

The extraction method commonly applied is known as the hot water method. In board outline, this method involves contacting the tar sand in a tumbler with hot water and steam. The Water is supplied at a temperature of about 180 F. and in a amount suflicient to produce a slurry containing about 20 to 25% by weight water. The steam is supplied in an amount sufficient to ensure that the slurry temperature is about 180 F. During slurrying, the bitumen films are ruptured and a preliminary separation of the sand grains and bitumen flecks takes place. At the same time, air bubbles are entrained in the slurry. More hot water is added to the slurry after it leaves the tumbler--typical1y this might raise the slurry water content to about 50%. The diluted slurry is then introduced into a separator cell containing a body of hot water. The contents of the cell are commonly maintained at about 180 F. In the cell, the bitumen particles, which have become attached to air bubbles, tend to rise to the surface of the water body and form an oily primary froth. This froth is recovered in a launder running around the rim of the cell. The coarse sand particles tend to sink to the bottom of the cell and are drawn oif as tailings. A middlings stream, comprising water, fine solids (minus 325 mesh) and some bitumen, is continuously withdrawn from the cell at a point intermediate its ends. This middlings stream is treated in a sub-aerated flotation cell to recover the contained bitumen in the form of secondary froth. The primary and secondary froths are combined and transferred into a holding tank to remove some of the contained solids and water by gravity settling.

All of the previously described process is extensively described in the literature and does not form part of the present invention. However, it does produce the feed stock, bitumen froth containing solids and water, which is treated in accordance with this process. While the composition of the froth can vary, it typically comprises 30% by weight water, solids and 60% bitumen.

Before the bitumen in the froth can be treated to recover salable products, it is necessary to remove most of ice the water. This has been done by diluting the froth with naphtha and centrifuging the product to remove the water. However, this prior art system involves expensive, highwear equipment. Alternatively, the froth has been heated indirectly in an exchanger with steam to vaporize the water; the Water vapor was subsequently flashed off. How ever, this process was not pursued, mainly because of the ioullilng of the exchanger tubes by clay left behind by the rot SUMMARY OF THE INVENTION The present invention is concerned with that type of thermal dehydration process wherein the bitumen froth is heated, to vaporize contained water, and is then flashed to separate the water vapor from the bitumen. The process has been developed with the objects of (l) avoiding the use of heat exchangers; (2) minimizing foaming and keeping it within predictable limits; and (3) keeping equipment costs low.

In accordance with the invention, dry bitumen is used as the vehicle for heating the froth. The bitumen is preheated to at least 300 F., preferably to a temperature in the range 600-700 F. It is mixed with the froth in a co-current flow mixer. The bitumen temperature, the amount of bitumen used, and the mixer residence time are selected having regard to the requirement that the desired amount of vaporization must be completed within the mixer. The mixer product is flashed in a flash zone of sufiicient volume and reduced pressure to produce water 'as overhead product and dry or substantially dry bitumen as the bottom product. Pa-rt of this bottom product may be recycled to the pre-heating step mentioned above.

The mixer itself may be a downflow vessel having staggered, vertically spaced plates which blank off the vessel cross section to restrict the flow area to about 20%. Alternatively, the mixer may be of the cyclone type, as was used in the example following hereinbelow.

The process is operated so that substantially all Water vaporization is carried out in the mixer. This is achieved by maintaining the temperature (Tm) of the mixer product stream about the same as the temperature (Tf) of the flash vessel bitumen stream. Preferably the temperature difference is maintained at less than 10 F. One way of doing this involves feeding the hot dry bitumen to the mixer at a constant rate and temperature, monitoring Tm and T and manipulating the rate at which froth is admitted to the mixer to maintain Tm equal to Tf.

The process is characterized by several advantages. By heating dry bitumen instead of froth, erosion of furnace tubes is reduced because of lower fluid velocities. The capital cost of the mixer and flash vessel is less than that of the equipment used in prior art processes. By carrying out vaporization in the mixer and maintaining Tm and T7 equal, it is found that the amount of foam generated in the flash vessel is reduced and its behaviour within the vessel is reasonably predictable; this latter characteristic permits one to select the smallest possible flash vessel for a given feed stock and operating conditions. Finally, the bitumen product contains only a small amount of water and this content is reasonably consistent over a prolonged period of operation.

Broadly stated, the invention comprises a thermal dehydration process for treating bitumen froth containing water, which process comprises: (a) heating substantially dry bitumen to a temperature greater than 300 F.; (b) mixing bitumen froth with a sufficient amount of the hot, dry bitumen of step (a) for a sufficiently long period of time to vaporize a predetermined amount of the water contained in the froth; and (c) flashing the product mixture to separate substantially all the vaporized water from the bitumen.

3 DESCRIPTION OF THE DRAWING In the drawing, FIG. 1 is a flow diagram illustrating the steps of the process.

DESCRIPTION OF THE PREFERRED EMBODIMENT (b) mixing bitumen froth with a sufiicient amount of the hot, dry bitumen from step (a) for a sufiiciently long period of time to vaporize a pre-determined amount of the water contained in the froth; and

(c) flashing the product mixture to separate substantially all the vaporized water from the bitumen.

2. The process as set forth in claim 1 wherein: the addition of bitumen froth to the mixing step is controlled to maintain the temperature of the product leaving the mixing step substantially equal to the temperature of the men, was fed, together with a hot, dry bitumen stream comprising /2% by weight water, solids and the blmmen Product from the flashmg P- balance bitumen, into a mixer 1. The relevant flow rates, A Pmcess separatlng Watfil' from bltumetl froth temperatures and analyses were as follows for a run of Which Comprises! hours: (a) heating substantially dry bitumen to a temperature I TABLE I Flow rates (lbs/hr.) Temperature, F. Analyses (percent water) Hot, dry Hot, dry Bitumen Bitumen Froth bitumen Water Froth bitumen Mixture product Water Froth product Water The mixer 1 comprised a series of six cyclone mixers. within the range 600 F. to 700 F.;

Each cyclone had a cylindrical top section, provided with (b) co-currently mixing bitumen froth with a sufficient a tangential inlet, and a conical bottom section. The top 5 amount of the hot, dry bitumen of step (a) for a section had a diameter of 4 inches and length of 6 inches. sufficiently long period of time to vaporize substan- The bottom section reduced over a length of 4 inches to tially all of the Water Contained in the froth;

an outlet diameter of 1 inch. The cyclones were connected (0) flashing the product mixture in a flash zone of by 1 inch diameter pipe. The inlet pressure to the first sufficient volume to permit of the Separation of cyclone was 55 p.s.i. and the outlet pressure from the last stanti'ally all the vaporized water from the bitumen cyclone was 15 p.s.i. The temperature of the product whereby all Overhead Product of Waterand a bottom stream was maintained t about 300 F product of substantially dry bitumen are produced The mixture was fed directly into a flash drum 2. This from the fl 20118; and vessel was cylindrical in shape and had an interior diar cycling part Of the bottom product to provide meter of 8 inches and a length of 38 feet. Its feed inlet was y bitumen for p located 10 feet from its top. The drum 2 was operated to The Process as Set forth in Claim 3 w e t e admaintain a fl id d th f b t 20 f t, a f di dition of one of the components mixed in the mixing step gagement zone bo t 8 f et i l h, d a pressure f is controlled to maintain the temperature of the product 4 p.s.i. The flow rates, temperatures and compositions of from p substantially equal to the temperature of the the product streams from the drum are given in- Table I. bottom Product from p As shown in Table I, the process was operated to main- The Process Set forth in Cla m 1 wherein: the tain the mixer product stream 'at the same temperature as bitumen froth and y bitumen are mixed the flash drum bottom product. This was done by manipucurrhntlylating the rate of froth feed to the mixer 1. It was found References Cited that the levels of the various layers within the drum 2 UNITED STATES PATENTS remained substantially constant under these conditions.

Our work has shown that the process must be operated 2550432 4/1951 Thompson 20811 with a recycle oil temperature between 300 F. and 700 2,775,541 12/1956 Karl 208-187 F. to vaporize the water at an acceptable rate. Preferably, 3,208,930 9/1965 Andtassy it should be operated between 600 F. and 700 F. Below 3,298,117 1/1967 9 600 F., the material recirculation rate becomes excessive; 7/1967 Blchard above 700 1 cracking of the bitumen begins to occur. 3331765 7/1967 C'fmevan et 208188 While the invention has been described in detail with 3338814 8/1967 P et 208 11 respect to a preferred embodiment, it will be understood 3466240 9/1969 Stemmetz 208-11 by those skilled in the art that various changes and modi- 3489672 1/1970 Schulman et a1 208-11 fications may be made without departing from the spirit 355698o 1/1971 Clark et a1 208-187 and scope of the invention and it is intended to cover all 3684699 8/1972 Vermeulen et 208 188 suc;l1/hchanges and modifications in the appended claims. DELBERT E GANTZ Primary Examiner at is claimed 1s. 1. A process for separating water from bitumen froth V. OKEEFE, Assistant Examiner which comprises:

(a) heating substantially dry bitumen to a temperature greater than 300 E;

US. Cl. X.R. 208-11, 187, 188